This mouse was probably dead for only a few hours. It had a couple of open wounds. It just goes to show how quickly insects start to feed and/or lay eggs or larvae on a carcass. Wasps, large black ants, and this fly were all vying for positions on the carcass.

From what I could find online, it seems there are only a few rare instances where certain flys lay maggots rather than eggs. I watched this fly closely as it placed itself over the mouse's mouth. The next thing I saw was the moving maggots. Is this type of fly able to do that, rather than depositing eggs?